Mississippian-age strata (360 to 325 million years ago), shown in light blue on the geologic map, are dominated by limestones, shales, and sandstones. A thick sequence of Mississippian limestone contains numerous oil reservoirs where it occurs beneath the surface; the same limestone is quarried where it occurs at the surface. The Reed quarry in western Kentucky, produces more limestone than any other quarry in the United States, from Mississippian strata (pictured above). The limestone also contains large cave systems, including the Mammoth Cave-Flint Ridge cave system, the longest in the world by many miles.